Effect of network structure from different processing conditions on the mechanical property of semi-crystalline polymers

2014 ◽  
Vol 1619 ◽  
Author(s):  
Xin Dong ◽  
David McDowell ◽  
Karl Jacob
Keyword(s):  
Mechanical Property ◽  
Strain Hardening ◽  
Mechanical Response ◽  
Tensile Deformation ◽  
Processing Condition ◽  
Constant Stress ◽  
Uniaxial Tensile ◽  
Initial Structure ◽  
Stress Strain ◽  
Strain Hardening Behavior

ABSTRACTSemi-crystalline structures were prepared from different processing condition. Biaxial oriented melt were crystallized at 375 K and atmospheric pressure for 10 nanoseconds (ns), to generate a lamellar semi-crystalline structure. Similar structures were also prepared from deformation of a cubic amorphous initial structure isothermally at 375 K. For comparison, two different thermostats, the constant stress (NPT) and constant volume (NVT) conditions were applied to the system during 10 ns of crystallization. The semi-crystalline samples shared common morphological features such as in the crystallinity, crystal orientation, lamellae thickness and density distribution, etc. However, during the subsequent uniaxial tensile deformation test of the samples to strain of 0.5, different stress-strain behaviors were demonstrated. By combining the observations of morphologies during deformation tests and analysis of the stress-strain curves, conclusions were made that the effectiveness of the network had a strong influence on the mechanical property and strain hardening behavior. The oriented network from the constant stress crystallization, owing to the taut chains, gave rise to optimal mechanical response with substantial strain-hardening.

scholarly journals An Experimental Study of the Tension-Compression Asymmetry of Extruded Ti-6.5Al-2Zr-1Mo-1V under Quasi-Static Conditions at High Temperature

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1299
Author(s):  
Chen Zhang ◽  
Dongsheng Li ◽  
Xiaoqiang Li ◽  
Yong Li
Keyword(s):  
High Temperature ◽  
Strain Hardening ◽  
Yield Stress ◽  
Mechanical Response ◽  
Tensile Deformation ◽  
Uniaxial Tensile ◽  
Tensile Direction ◽  
Stress Asymmetry ◽  
Static Conditions ◽  
Tension Compression Asymmetry

The tension-compression asymmetry (TCA) behavior of an extruded titanium alloy at high temperatures has been investigated experimentally in this study. Uniaxial tensile and compressive tests were conducted from 923 to 1023 K with various strain rates under quasi-static conditions. The corresponding yield stress and asymmetric strain hardening behavior were obtained and analyzed. In addition, the microstructure at different temperatures and stress states indicates that the extruded TA15 profile exhibits a significant yield stress asymmetry at different testing temperatures. The flow stress and yield stress during tension are greater than compression. The yield stress asymmetry decreases with the increase in temperature. The alloy also exhibits TCA behavior on the strain hardening rate. Its mechanical response during compression is more sensitive than tension. A dynamic recrystallization phenomenon is observed instead of twin generated in tension and compression under high-temperature quasi-static conditions. The grains are elongated along the tensile direction and deformed by about 45° along the compressive load axis. Finally, the TCA of Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy is due to slip displacement. The tensile deformation activates basal <a>, prismatic <a> and pyramidal <c + a> slip modes, while the compressive deformation activates only prismatic <a> and pyramidal <c + a> slip modes.

Chain Entanglements and Mechanical Behavior of High Density Polyethylene

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Joy J. Cheng ◽  
José A. Alvarado-Contreras ◽  
Maria A. Polak ◽  
Alexander Penlidis
Keyword(s):  
Molecular Weight ◽  
Strain Hardening ◽  
Amorphous Phase ◽  
Tensile Deformation ◽  
Micromechanical Modeling ◽  
Uniaxial Tensile ◽  
Hardening Behavior ◽  
Strain Hardening Behavior ◽  
Chain Entanglements

It has long been suspected that physical chain entanglements in the amorphous phase affect the strain hardening behavior of polyethylene. The precise number of chain entanglements in solid polyethylene cannot be measured using any current techniques. Since entanglements in the melt state are known to be preserved in the polymer upon solidification, determination of the molecular weight between entanglements (Me) is used as a measure of chain entanglements for polyethylene. A decrease in molecular weight between entanglements means an increase in the number of entanglements in the polymer. As the Me value decreases, increasing tensile strain hardening of polyethylene is observed. In addition to experimental work, parallel micromechanical modeling was carried out to study the entanglement effect in uniaxial tensile deformation. The model was able to shed more light over the earlier empirical speculations. By combining experimental observations and modeling results, the presence of physical chain entanglements in the amorphous phase was demonstrated to be the controlling factor in strain hardening behavior of polyethylene.

scholarly journals Ability of Constitutive Models to Characterize the Temperature Dependence of Rubber Hyperelasticity and to Predict the Stress-Strain Behavior of Filled Rubber under Different Defor Mation States

Polymers ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 369
Author(s):  
Xintao Fu ◽  
Zepeng Wang ◽  
Lianxiang Ma
Keyword(s):  
Experimental Data ◽  
Temperature Dependence ◽  
Mechanical Response ◽  
Constitutive Models ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Chain Model ◽  
Stress Strain ◽  
Filled Rubber ◽  
Yeoh Model

In this paper, some representative hyperelastic constitutive models of rubber materials were reviewed from the perspectives of molecular chain network statistical mechanics and continuum mechanics. Based on the advantages of existing models, an improved constitutive model was developed, and the stress–strain relationship was derived. Uniaxial tensile tests were performed on two types of filled tire compounds at different temperatures. The physical phenomena related to rubber deformation were analyzed, and the temperature dependence of the mechanical behavior of filled rubber in a larger deformation range (150% strain) was revealed from multiple angles. Based on the experimental data, the ability of several models to describe the stress–strain mechanical response of carbon black filled compound was studied, and the application limitations of some constitutive models were revealed. Combined with the experimental data, the ability of Yeoh model, Ogden model (n = 3), and improved eight-chain model to characterize the temperature dependence was studied, and the laws of temperature dependence of their parameters were revealed. By fitting the uniaxial tensile test data and comparing it with the Yeoh model, the improved eight-chain model was proved to have a better ability to predict the hyperelastic behavior of rubber materials under different deformation states. Finally, the improved eight-chain model was successfully applied to finite element analysis (FEA) and compared with the experimental data. It was found that the improved eight-chain model can accurately describe the stress–strain characteristics of filled rubber.

scholarly journals Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

2017 ◽  
Vol 114 (16) ◽  
pp. E3170-E3177 ◽  
Author(s):  
H. Samet Varol ◽  
Fanlong Meng ◽  
Babak Hosseinkhani ◽  
Christian Malm ◽  
Daniel Bonn ◽  
...  
Keyword(s):  
Strain Hardening ◽  
Polymer Nanocomposites ◽  
Nonlinear Elasticity ◽  
Volume Fraction ◽  
Uniaxial Tensile ◽  
Large Strains ◽  
Chain Alignment ◽  
Strain Hardening Behavior ◽  
Polymer Chain Alignment ◽  
Nonlinear Hardening

Polymer nanocomposites—materials in which a polymer matrix is blended with nanoparticles (or fillers)—strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently.

Mechanical Properties and Strain Transfer Behavior of Molybdenum Ditelluride (MoTe2) Thin Films

2021 ◽  
pp. 1-31
Author(s):  
Shoieb Ahmed Chowdhury ◽  
Katherine Inzani ◽  
Tara Pena ◽  
Aditya Dey ◽  
Stephen M. Wu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Phase Change ◽  
Density Functional ◽  
Mechanical Response ◽  
Interatomic Potential ◽  
Tensile Deformation ◽  
Random Search ◽  
Mechanical Strain ◽  
Uniaxial Tensile ◽  
Strain Transfer

Abstract Transition metal dichalcogenides (TMDs) offer superior properties over conventional materials in many areas such as in electronic devices. In recent years, TMDs have been shown to display a phase switching mechanism under the application of external mechanical strain, making them exciting candidates for phase change transistors. Molybdenum ditelluride (MoTe2) is one such material that has been engineered as a strain-based phase change transistor. In this work, we explore various aspects of the mechanical properties of this material by a suite of computational and experimental approaches. Firstly, we present parameterization of an interatomic potential for modeling monolayer as well as multilayered MoTe2 films. For generating the empirical potential parameter set, we fit results from Density Functional Theory calculations using a random search algorithm called particle swarm optimization. The potential closely predicts structural properties, elastic constants, and vibrational frequencies of MoTe2 indicating a reliable fit. Our simulated mechanical response matches earlier larger scale experimental nanoindentation results with excellent prediction of fracture points. Simulation of uniaxial tensile deformation by Molecular Dynamics shows the complete non-linear stress-strain response up to failure. Mechanical behavior, including failure properties, exhibits directional anisotropy due to the variation of bond alignments with crystal orientation. Furthermore, we show the deterioration of mechanical properties with increasing temperature. Finally, we present computational and experimental evidence of an extended c-axis strain transfer length in MoTe2 compared to TMDs with smaller chalcogen atoms.

Atomistic Study on Nano Stress-Strain Curves of α-Fe

1997 ◽  
Vol 492 ◽  
Author(s):  
Shenyang Hu ◽  
Matthias Ludwig ◽  
Liam Farrissey ◽  
Siegfried Schmauder
Keyword(s):  
Boundary Conditions ◽  
Tensile Deformation ◽  
Tensile Axis ◽  
Plane Boundary ◽  
Uniaxial Tensile ◽  
Stress Strain ◽  
Fracture Characteristics ◽  
Deformation And Fracture ◽  
Dislocation Movement ◽  
Atomistic Study

ABSTRACTThe atomistic processes and stress-strain-curves during uniaxial tensile deformation of a single α-Fe nanocrystal have been studied with the molecular static method. Periodic boundary conditions are imposed along one direction perpendicular to the tensile axis to model plane strain conditions. The effects of the model sizes in plane, boundary conditions and crystal orientations on the stress-strain curves are systematically analyzed. Various deformation evidences such as dislocation movement, dislocation piling up and twinning are clearly observed. The deformation and fracture characteristics of a-Fe and their dependencies on the boundary conditions are investigated.

scholarly journals Effect of Discontinuous Yielding on the Strain Hardening Behavior of Fine-Grained Twinning-Induced Plasticity Steel

2021 ◽  
Vol 8 ◽  
Author(s):  
Singon Kang ◽  
Sujin Jeong ◽  
Yeon-Sang Ahn
Keyword(s):  
Strain Hardening ◽  
Tensile Deformation ◽  
Early Stage ◽  
Image Correlation ◽  
Localized Deformation ◽  
Fine Grained ◽  
Cooling Conditions ◽  
Strain Hardening Behavior ◽  
Strain Hardening Rate

The yielding of a high Mn twinning-induced plasticity steel was examined in three fine-grained specimens recrystallized at 700°C for 5 min with different cooling conditions. While the stress-strain curves of furnace-cooled and air-cooled specimens exhibit a stress drop at yielding, the drop was not observed in the water-quenched specimen. A simple analysis of the displacement data indicates the occurrence of localized deformation at the beginning of the plastic deformation in the three tensile specimens with different cooling conditions. The localized deformation of all three specimens was confirmed as Lüders strain by digital image correlation (DIC) analysis. Based on this observation, the role of yielding behavior on the strain hardening rate evolution at an early stage of the tensile deformation was discussed.

A full-range stress-strain model for metallic materials depicting non-linear strain-hardening behavior

2020 ◽  
pp. 030932472095779
Author(s):  
Digendranath Swain ◽  
S Karthigai Selvan ◽  
Binu P Thomas ◽  
Ahmedul K Asraff ◽  
Jeby Philip
Keyword(s):  
Constitutive Model ◽  
Strain Hardening ◽  
Image Correlation ◽  
Linear Strain ◽  
Stress Strain ◽  
Material Parameters ◽  
Hardening Behavior ◽  
Non Linear ◽  
Strain Hardening Behavior ◽  
Strain Model

Ramberg-Osgood (R-O) type stress-strain models are commonly employed during elasto-plastic analysis of metals. Recently, 2-stage and 3-stage R-O variant models have been proposed to replicate stress-strain behavior under large plastic deformation. The complexity of these models increases with the addition of each stage. Moreover, these models have considered deformation till necking only. In this paper, a simplistic multi-stage constitutive model is proposed to capture the strain-hardening non-linearity shown by metals including its post necking behavior. The constitutive parameters of the proposed stress-strain model can be determined using only elastic modulus and yield strength. 3-D digital image correlation was used as an experimental tool for measuring full-field strains on the specimens, which were subsequently utilized to obtain the material parameters. Our constitutive model is demonstrated with an aerospace-grade stainless steel AISI 321 wherein deformation response averaged over the gauge length (GL) and at a local necking zone are compared. The resulting averaged and local material parameters obtained from the proposed model provide interesting insights into the pre and post necking deformation behavior. Our constitutive model would be useful for characterizing highly ductile metals which may or may not depict non-linear strain hardening behavior including their post necking deformations.

Effect of Temperatures on Tensile of Aluminium Thin Films

2012 ◽  
Vol 528 ◽  
pp. 135-139 ◽  
Author(s):  
Qiao Neng Guo ◽  
Shi E Yang ◽  
Qiang Sun ◽  
Yu Jia ◽  
Yu Ping Huo
Keyword(s):  
Thin Films ◽  
Molecular Dynamics ◽  
Maximum Stress ◽  
Tensile Deformation ◽  
Uniaxial Extension ◽  
Strain Curve ◽  
Local Maximum ◽  
Temperature Curve ◽  
Uniaxial Tensile ◽  
Stress Strain

The mechanical process of single-crystal aluminium thin films under uniaxial tensile strain was simulated with molecular dynamics method at different temperature. The stress–strain curve and potential energy–strain curve of thin aluminium film under uniaxial tensile deformation were obtained by molecular dynamics simulations. With the changes of sample temperatures in uniaxial extension, the variation characteristics of stress–strain curves are alike at the elastic stage and different at the plastic one below and above 370 K, respectively. From the stress–strain curves, we gained the first local maximum stress-temperature curve and the strain at the first local maximum stress-temperature curve, and found that the strange temperature dependence of first local maximum stress: when the temperature is above 370 K, the stress goes down quickly with temperature, and when below 370 K, it descends slowly. With increasing temperature, the difference between two strain values corresponding to two maximal potential energies changes slowly below and above 370K but it goes up quickly about 370K. By these dependences, we have identified the critical temperature （370K） for the transition of plastic flow mechanism.

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